Secret telecommunication



Jan. 15; 1946. G. F, VAN mSSEL 2,393,224

SECRET TELECOMMUNI CAT ION Filed Aug. 23, 1943 2 Sheets-Sheet 1 5500CYCL 5 30o CYClf-S e000 |3600 @UFS 6300 2 sneetsTshet 2 Filed Aug. 23,1943 Patented Jan. 15, 1946 UNITED STATES PATENT OFFICE 2,393,224 SECRETTELECOMMUNICATIN Gysbert Frans Van Dlssel, New York, N. Y. ApplicationAugust 23, 1943, Serial No. 499,662

' (ci. 17o-1.5)

21 Claims.

'I'he present invention relates to communicating systems and moreparticularly to secret telecommunication systems.

The field of secret telecommunications may be divided into three groups,of which the first consists of systems which make the transmittedcommunication (telephone or telegraphic) unintelligible to those personspossessing the ordinary receiving sets constructed to receive normaltelecommunication, but easily transformable into intelligentcommunication with the help of some simple technical equipment. Forexample, in-

version of the` speech by means of a modulation on a low frequencycarrier. The second group consists of systems transmittingunintelligible communications which can be made intelligible only bymeans of complicated manipulations requiring special technicalequipment, plus considerable engineering skill. For example, breaking upof the speech frequency band in parts by means of filters and shiftingthese parts by means of a modulation on a low frequency carrier. Thethird group comprehends the use of a selected secret key with either ofthe first and second groups, so that the transformation of thetransmission into intelligent speech will not only require considerabletechnical equipment and engineering skill, but also the knowledge of theselected key, which latter may be fixed or variable. This key can be somixed up in the communication as to makethe finding of it practicallyimpossible. For example, superposing' of the speech frequency band byother bands masking or screening the speech and separating thesesuperposed bands at the reception by means of special devices.

Some of the objects of the present invention `are to provide an improvedsystem of telecommunication; to provide such a system wherein thetransmitted communication is unintelligible except to those for whom itis intended; to provide a system of telecommunication wherein a secretkey not only renders the speech or message unintelligible to all exceptthose having knowledge of the key, but is such as to make the nding ofthe key practically impossible to anyone; to provide a secrettransmission system wherein a novel screening method using movablescreening frequency bands is used; to provide a telecommunicating systemwherein the secrecy of the transmitted message is made possible by themoving of screening bands in ac-v cordance with a predetermined selectedpattern;

to provide a secret telecommunication system wherein the secretcontrolling key has two possible variables, namely, (a) the frequency ofmodulation of the screen spectrum, and (b) the pattern of the changein'frequency; to provide a telecommunication system wherein the secrecyis obtained by using a plurality of moving screens;

and to provide otherimprovements as will hereinafter appear.

In the accompanying drawings, F18. l is a schematic showing of thespeech and screen spectrums and related frequencies according to onemethod of the invention; Fis. 2 is a schematic showing of the separationof the speech band into a plurality of components in conjunction with a.method employing two moving screens; Fig. 3 is a schematic showing ofanother method of the invention wherein a reversed speech band forms thescreening medium; Fig. 4 is a schematic showing of another method of theinvention wherein the screening spectrum ls formed by oppositely movingscreens according to a predetermined rhythm; and Fig. 5 is a diagramillustrating one form of transmitting and receiving stations for sendingand receiving the locally produced low frequency carrier on a highfrequency carrier masked or screened in accordance with the method ofthe invention.

Referring to Fig. 1 of the drawings, it is assumed that the speechfrequency band to bev screened covers from 300 to 3000 cycles per secondwhilethe low frequency carrier is taken as 3300 cycles per second. Thiscarrier is represented by the upper light broken line. When the speechfrequency is modulated on this carrier, a speech spectrum will appearwith two side bands covering frequencies of 300 to 3000 cycles persecond for the lower side band and 3600 to 6300 cycles per second forthe` higher side band. The modulated carrier is now passed through asuitable filter and the carrier filtered out so that only the two sidebands remain. Obviously, wherever speech is mentioned it will beunderstood to comprise any form of communication, whether signals orspeech, although for ease and speed of transmission and reception actualspeech is preferred.

In the following, certain of the terms used are defined as follows: aspeech band is to befunderstood as a. frequency band containing theaudible frequencies and is assumed as limited to a band from 300 to 3000cycles per second; a speech spectrum is to be understood as a speechband modulated on a carrier producing next to the carrier two sidebands; a screen band" is to be understood as a -frequency bandcontaining audible frequencies destined to cover or screen a. speechband, and such screen band may be smaller than, equal to, or largerthan; the speech band; and a screen spectrum is to be understood as ascreen band modulated on a carrier producing next to the carrier twoside bands.

In order to produce a screening spectrum, it is assumed that a carrierof 3300 cycles per second is taken which is the same frequency as thecarrier chosen for the speech spectrum. The screening band to bemodulated on this carrier may be '2 Vi'rom 300 to 3000 cycles persecond. When this screening band is modulated on the carrier of 3300cycles per second, indicated by the lower heavy broken line, the resultwill be a screen spectrum consisting of the carrier and tw`o side bandsrespectively of 300 to 3000 cycles per second and 3600 to 6300 cyclespersecond which when superposed on the two speech side bands will coverand screen both and render the speech unintelligible to the unpreparedauditor.

For the purpose of making the speech undecipherable as well as initiallyunintelligible, the carrier frequency of the screen spectrum is given anoscillation or swing which illustrati"ely may cause it to vary between3100 and 3500 cycles per second. The degree of swing is one of thevariants contributing to the modus or pattern of movement, while therate of swing or oscillation and the actual wave form followed by theswing or movement is another variant contributing to `the modus orpattern of movement. Generally speaking, the wave form itself is themajor factor in establishing impenetrability of the screen. Assuming theswing of 200 cycles per second on each side of the carrier frequency of3300 cycles per second mentioned, then the two side bands respectivelywillhave an oscillatory movement between 100 and 2800 cycles per secondand between 500 and 3200 cycles per second for the lower side, andbetween 3800 and-6500 ycycles per second and 3400 and 6100 cycles persecond for the higher side. The result will be a totally covered bandfrom 100 to 6500 cycles per second with a gap off200 cycles per secondbetween 32100 and 3400 cycles per second in which no speech or screenband frequencies exist. When this moving screen is superposed on theside bands of the speech remaining after filtering out the speechcarrier, the speech becomes thereby both unintelllgible andundecipherable.

From the foregoing, it will be evident that while the total spectrum maybe transmitted in any manner, as by wire or cable, and through the etherby means of a high frequency carrier, and in all cases can be restoredat the reception with a normal receiver, an uninformed or even a.partially but incompletely prepared and informed observer will be unableto decipher the transmitted speech message, even though the observer mayknow the separating mechanism by which the screened speech is separatedfrom the screen. In the system just described. there are three elementsnecessary for an observer to know with exactness in order to effectuatethe separation; namely, (1) the carrier frequency offthe'speech, (2) thecarrier frequency of the screen, and (3) the modus ofthe movement of thescreen. For example, from the symmetrical aspect of the speetrum theobserver might draw the conclusion that the first carrier frequency isin the middle of the gap 3200 to 3400 or 3300 cycles. The observer mighteven suppose that the second carrier frequency is separated from thei'lrst by a difference .of only 200 cycles per second, and thus try outall the possible frequencies within those limits. However, there stillremains unknown the modus of the movement of the screen 'and this thespe cifically uninformed'observer orauditor cannot find by `any analysisof the received spectrum.v

As a modification of the foregoing method, the screening spectrum may beproduced by a carrier frequency which is out of phase with the carrierfrequency of .the speech spectrum, and this out of phase frequency maybe caused to swing or oscillate in a predetermined manner.

As a means for even hiding the carrier frequency of the speech spectrumand the carrier frequencyof the screening spectrum, it is technicallypossible to make the total spectrum dissymmetrical inrelation to thecarriers of the screened and screening spectrums, assuming that one andthe same frequency is used for both with a phase difference. This can bedone by adding to the speech spectrum and the screening spectrum, athird spectrum, a so-called "decentering spectrum which lextends one ofthe side bands with respect to the other. The same decentering resultmay also be obtained by choosing for the carrier frequency of thescreening spectrum a frequency differing considerably from the frequencyof the screened spectrum.v The total result of both methods will be adecenterlng spectrum. It will become extremely difficult for anuninformed observer to find out the frequencies of the carriers. To addto the difficulties of such an observer, a third variable may be added;namely, the varying of the phase difference between the carrier of thespeech or screened spectrum. and the carrier of the screening spectrum.Furthermore, the position of the screened and the screening spectrum maybe inversed, whereby the speech spectrum will then become the movingspectrum and the screening spectrum the fixed spectrum, while all otherconditions remain the same. The screening spectrum may also be smalleror larger than the screened spectrum and may be derived from thescreened spectrum itself`or may be of extraneous origin.

In order that the low frequency carriers of screened and screeningSpectrums can be reproduced at the receiving station, means such as twincrystals are, provided to synchronise the ,signal from the transmitterto the receiver.

While in the foregoing a. single screen has been d@ described andemphasized, the quantity of screens may be more than one, the totalbeing limited only by practical conditions. In using differentfrequencies for the carriers of the screened and. screening spectrumsthe maximum is also limited by practical considerations. The

movement of these different screens may be linked up in one way oranother electrically or may be completely independent. For instance,when two screens are applied it may be assumed that they move in thesame rhythm butin opposite directions, or simply with a phase differenceusing the same pattern, or moved by two independent and unrelateddifferent patterns.

The pattern itself may consist in any form of oscillation or periodicalor aperiodical function conceivable, from the pure sinusoidaloscillation to the most arbitrary form, e. g., square, triangle,zig-zag, relaxation forms containing harmonics, etc. 'I'hese periodicalor analogous functions may be derived directly fromv the high frequencytransmission carrier or from an extraneous source. In the last caseprovisions must be taken for a synchronising signal from transmitter toreceiver. The carrier and the synchronizing signal or only the carrierand only the synchronous signal may be transmitted in the gap rbetweenthe two side bands, symmetrical or dissymmetrical, and may in their turnbe masked or screened by a. great quantity of other frequencies at aminimum distance.

In such a case, the unprepared and specifically unknowing observer willbe aware of a gap containing a plurality of waves out-of which he has 6to choosea combination of at least two waves,

one being the lowfrequency carrier, the other the sychronislng signalfor the screen movements.

It may be clear that the increase of screens will V increase the'possible combinations. However, it

any element oi the form of the movement. This element of form cannot beselected by analysis of the transmitted spectrum. l

The above described methods require a total frequency bend which may begeaterqthan the Vtwo side bands and the gap, as'the movement of thescreens may extend the side bands. This means in practice for instance,a total band of about 7000 cycles per second, assuming the respectiveside bands have a width o1 3000 cycles per second, or about 6000 cyclesper second. with respective side bands from 300 to 2700 cycles persecond.

Actually, most transmitters permit the transmission of side bands of awidth of 300 to 7000 cycles per second. However, in the case that theside bands may not be larger than 3000 cycles. the following systems maybe used. The original speech band will be broken in two or three parts.equal or unequal, by means of filters, e. g., with a spectrum 300 to3000 cycles per second. For instance. from 300 to 1200, 1200 tol 2100,2100 to 3100 cycles per second, as shown in Fig. 2.

By means of a modulation of a low frequency carrier of 2400 cycles persecond, the band from 1200 to 2100 cycles per second can be reversed andreduced to 300 to 1200 cycles per second. The same can be done withtheband from 2100 to 3000 cycles per second using a low frequency carrierof 3300 cycles per second. See Fig. 2. Thus, the total speech spectrumby transposition, comprises three different spectrums, each from 300 to1200 cycles per second, and comprising, illustratively a.. Fixedspectrum to be screened b. First screen C. Second screen Each of thecarriers of the two screens will be given a movement, which movementsmay be linked up electrically or may be completely independent.

At the reception, the abc spectrums caribe separated and built up againin the reverse way, for spectrum b, with a modulation on a carrier of2400 cycles per second will become again 1200 to 2100 cycles per second,the spectrum c with a modulation on a. carrier of 3300 cycles per secondwill become 2100 to 3000 cycles per second. b and c together with a givethe spectrum extending from 300 to 3000 cycles per second in therearranged and reconstituted speech.

Fig. 3 represents the simplest form of device and system in which aspeech band from 300 to 3000 cycles per second is impressed upon acarrier of 3300 cycles per second while the moving screen comprises themodulation of a moving carrier of 3300 cycles per second by an inversionof the speech band of 300 to 3000 cycles per second.

In the form of invention of Fig. 4, a low frequency carrier of say 3300cycles modulated with the speech band, 300 to 3000 cycles per secondforms the speech spectrum, while the screen band consists of thereversed speech band of 300 to 3000 cycles per second. 'I'his screenband is modulated on a low frequency carrier of 3300 cycles persecond'having the same frequency as the carrier of the speech spectrumbut a phase difference of +90. A second screen spectrum is formed bymodulating the same screen band on.a.

carrier having the same frequency as the carrier of the speech spectrumbut with a phase difference of -90. The key to the opposite movements ofthe screening spectra may be taken as terval cariche one harmonic, forinstancel which Y Y' automatically changes to another harmonic with theending of the said tirneinterval. The intervals may be by hours orsub-divisions thereof or by days or sub-divisions thereof, according tonecesn sities. These three modulated carriers are mixed giving the totalspectrum. The resulting movement of the frequencies of the lower andupper side bands is in opposite directions because the impressed screenis on two carriers with a phase difference of 180 and having oppositelymoving directions. The two side bands AB and CD are transmitted with thelow frequency carrier or modulated on a high frequency transmittingcarrier. At the reception the low frequency band ABCD with carrier 3000cycles per second is first restored and the moving screen and fixedspeech screen separated. It is understood that in all cases mentionedsuch a separation can be effectuated by means of devices enabling theseparation of two or more modulated waves having the same carrierfrequency but different phases,

. such as Carsons balanced demodulator, or other balanced arrangementsconstituted of copperoxide or coppersulfide cells or seleniumrectifiers, or by means 0f one of the devices described in the patentsto Dr. Leonide Gabrilovitch, No. 22.110.500 and No. 2,295,207. Thesedevices also permit the utilization of two or more modulated carriers ofdifferent frequencies so close together that their s idebands overlapeach other..

In order to obtain more and more adequate protection, the followingmeans are proposed:

1-a) A second screen making the side bands unsymmetrical by extendingone of them.

(1 -b) Masking or screening the low frequency carrier by means of aplurality of waves in the gap differing in frequency the practicalminimum necessary for their separation.

(1 -c) Giving the movement a frequency independent of the low frequencycarrier.

(l-d) Giving the movement a. special pattern.

An example of a. system may be given as folows:

(a) A speech frequency band of 300 to 2700 cycles per second has -to betransmitted.

(b) This speech spectrum is first divided in two equal parts, 300 to1500 and 1500 to 2700 cycles per second.

(c) One of these, the part 1500 to 2700 cycles per second, is reversedby means of modulation on a carrier of 3000 cycles per second. Thisproduces two side bands of 300 to 1500 and 4500 to 5,700 cycles persecond. The 300 to 1500 cycles per second band is filtered out, beingthe reversed 1500 to 2700 cycles per second band of b.

(d) A carrier of 1500 cycles per second is produced. This carrier may bederived from the high frequency carrier mentioned under "j" mentionedhereinafter, or it may be transmitted on that high frequency carrierwith a masking spectrum, produced by means of twin crystals or asynchronizing signal.

(e) This low frequency carrier is first divided in three parts (1) Thesame carrier with phase a.

' (2) The same carrier withphase a|'90.

(3) The same carrier frequency modulated with a frequency variation of200 cycles per second or less.

- (f) For e-3 is used for modulation a part of 300 to 1500 cycles persecond speech band (sub b" above) being 500 to 1300 c ycles per second.

(g) On carrier "e-1 is modulated the band l 300'to 1500 cycles persecond sub"b, notf'reversed.

On carrier e-2A is modulated the band 300 to 1500 cycles per second sub"c, reversed.

On carrier "e-3 is modulated the band 500 to 1300 cycles per second sub,f, with a deviation to both sides of 200 cycles per second or less thusproducing a band of 300 to 1500 cycles per second.

The speed and form .of the modulation form the key.

(h) The three modulated carriers sub e-1,

e-2, e-3, are then superposed and modu' lated together on a lowfrequency carrier of 1500 cycles per second (sub. d above) producing twoside bands of (l.) 300 to 1500 cycles per second not reversed.

. (2) 2100 to 3300 cycles per second reversed.

(i) The, gapof 1500 to 2100 cycles per second between side bands h-1 andh-2 may be filtered out in the case the low frequency carrier may bederived from the high frequency carrier sub j below, or be filled with amasking spectrum, covering the two frequency carriers off- 1500 cyclesper second.

(j) This total spectrum of "h--1 and h2 totalling 300 to 3300 cycles persecond with or without gap is then modulated on a high frequencytransmission carrier, for transmission.

Having thus described 'my invention, I claim: 1. The method oftransmitting secret telecommunication, which consists in modulating acarrier of predetermined frequencyto form a speech spectrum, modulatinga. second carrier of predetermined frequency to form a screen spectrum,superposing one spectrum on the other to completely cover one spectrum-with the other, and varying the position of one of the spectra inrelation to the iixed position of the other.

2. The method of transmitting secret telecommunication, which consistsin modulating a carrier of predetermined frequency to form a speechspectrum, modulating a second carrier of pre-v determined frequency toform a screen spectrum, superposing one spectrum on the other tocompletely eover'one spectrum with'the other, and varying the positionof the two spectra in relation to their original position.

3. The method of transmitting secret'telecommunication, which consistsinmodulating a carrier of predetermined frequency to form 'a speechspectrum, modulating a second carrier of predetermined frequency to forma screen spectrum. superposing the screen spectrum on and completelycovering the speech spectrum, and varying the position of the screeningspectrum in relation to the fixed position of the speech spectrum.

4. The method of transmitting secret telecommunication, which consistsin modulating a carrier of predetermined frequency to form a speechspectrum, modulating a second carrier of predetermined frequency to forma screen spectrum, superposing the screen spectrum on and completelycovering the speech spectrum, and subjecting the position of thescreening spectrum to a rhythmic movement of predetermined frequency.

5. 'I'he method of transmitting secret telecommunication, 'whichconsists in modulating a carrier of predetermined frequency to form aspeech spectrum, modulating a second carrier of predetermined frequencyto form a lscreen spectrum, superposing the screen spectrum on andcompletely covering the speech spectrum, andv subjecting the position ofthe screening spectrum to a rhythmic movement of predetermined frequencyand pattern.

6. The method of transmitting secret telecommunication, which consistsin modulating a carrier of predetermined frequencyto form a speechspectrum, modulating a second carrier of predetermined frequency to forma screen spectrum,

(o) By means of filtering are separated the part 300 to 1500 cycles persecond, non-reversed equal to 300 to 1500 cycles per second sub b, orsub 71, and the partv 2100 to 3300 cycles persecond (reversed) equal tosub lb-2.

(12)' Part 2100 to 3300 cycles per second is then reversed by modulatingon a carrier of 4500 cycles per second, this gives a non-reversed bandof 1500 to 2700 cycles per second.

(q) The two bands 300 to 1500 cycles nonreversed sub o and 1500 lto 2700cycles per second non-reversed sub p, give together the normal speechband of 300 to 2700 cycles per second.

Fig. 5 graphically illustrates one arrangement of the apparatus forsending and receiving secret communications in accordance with thepresent invention, including the frequency producing means, lters, andmodulation means.

superposing the screen spectrum on and completely covering the speechspectrum, and subjecting the position of the screening spectrum to arhythmic movement of predetermined pattern.

7. The method of transmitting secret telecommunication, which consistsin modulating a carrier of predetermined frequency to form a speechspectrum, modulating a second carrier of the same frequency as the firstcarrier but differing in phase .to form a screen spectrum, superposingthe screen spectrum on and completely covering the speech spectrum, andvarying the position of one of the spectra in relation to the fixedposition of the other spectrum.

8. 'I'he method of transmitting secret telecommunications, whichconsists in modulating a carrier of predetermined frequency to form afixed screening spectrum, modulating a second carrier of predeterminedfrequency to form a speech spectrum of the same frequencycharacteristics as the screen spectrum, superposing the one spectrum onthe other spectrum, and subjecting the position of the speech spectrumto a rhythmic movement of predetermined frequency.

9. The method of transmitting secret telecomf munication, which consistsin modulating a carrier of predetermined frequency to. form a fixedscreening spectrum, modulating a. second carrier of predeterminedfrequency to form a speech spectruml of the same frequencycharacteristics as the screen spectrum', superposing the one spectrum onthe other spectrum, and subjecting the position of the speech spectrumto a rhythmic movement of predetermined frequency and pattern.

10. The method of transmitting secret telecommunications, which consistsin modulating a carrier of predetermined frequency to form a xedscreening spectrum, modulating a second carrier of predeterminedfrequency to form a speech tering out the carrier to leave the upper andlower side bands of the speech spectrum, modulating a second carrier 'oflow frequency to form a screening spectrum of the same frequencycharacteristics as the speech characteristics, varying the frequency ofthe carrier Dfor one of the spectra, and superposing the moving spectrumon and rhythmically overlapping the upper' and lower side bands of thefixed spectrum.

12. The method of transmitting secret telecommunication, which consistsin modulating a low frequency carrier to form a speech spectrum of upperand lower side bands, filtering out the carrier and one of the sidebands, modulating a second carrier to form a speech spectrum with onereversed speech band, varying the position of this spectrum, andsuperposing the reversed speech band of this spectrum on the remainingside band after having filtered out the carrier and the not reversedside band.

13. The method of transmitting secret telecommunication, which consistsin modulating a low frequency carrier to form a speech spectrum,modulating simultaneously two different low frequency carriers,superposing the thus produced screen spectra upon and completelycovering said speech spectrum, and imparting rhythmic movement to thetwo superposed screen spectra respectively in opposite directions toscreen the speech spectrum.

14. The method of transmitting secret telecommunication, which consistsin modulating a low frequency carrier to form a speech spectrum,modulating simultaneously two low frequency carriers of different phase,superposing the thus produced two screen spectra upon and completelycovering said speech spectrum. and imparting a rhythmic movement to eachof the last mentioned carriers in the same direction but differing infrequency.

15. The method of transmitting secret telecommunications, which consistsin modulating a carrier of predetermined frequency to form a speechspectrum, modulating a second carrier of predetermined frequency to forma screen spectrum, superposing one spectrum on the other to completelycover one spectrum with the other, and varying the position of one ofthe spectra as a function of a sub-harmonic of one of the carriers.

16. The method of transmitting secret telecommunications, which consistsin modulating a carrier of predetermined frequency to form a speechspectrum, modulating a second carrier of predetermined frequency to forma screen spectrum, superposing one spectrum on the other to completelycover one spectrum with the other, varying the frequency of one of thecarriers according toV a key pattern, and impressing the total spectrumon a high frequency carrier comprising a harmonic function of one ofsaid modulated carriers.

17. The method of transmitting secret telecommunications which consistsin modulating a carrier of predetermined frequency to form a speechspectrum, modulating a second carrier of predetermined frequency to forma screen spectrum, filtering out one of said carriers, superposing onespectrum on the other, varying the frequency of the remaining carrieraccording to a predetermined pattern of oscillation, then impressing thetotalspectra on a transmission circuit.

18. The method of transmitting secret telecommunications, which consistsin modulating a carrier of predetermined frequency to form a speechspectrum, in modulating a second carrier of predetermined frequency toform a first screen spectrum, in modulating a third carrier ofpredetermined frequency to form a second screen spectrum, in superposingall of the spectra, in varying the position of at least one spectrumaccording to a predetermined pattern, and in then transmitting the totalspectra.

19. The method of transmitting secret telecommunication, which consistsin modulating a carrier of predetermined frequency to form a speechspectrum, modulating a second carrier of predetermined frequency toform* a screen spectrum, superposing one spectrum on the other tocompletely cover one spectrum with the other, and varying the positionof one of the spectra to cause the side bands thereof to substantiallyoverlap to form a continuous spectrum having no gap.

20. The method of transmitting secret telecommunication, which consistsin modulating a carrier of predetermined frequency to form a speechspectrum, modulating a second-carrier of predetermined frequency to forma screen spectrum, superposing one spectrum on the other to completelycover one spectrum with the other, varying the position of one of thespectra, and causing the screening spectrum to be dissymmetrical so aseffectively to extend one of the side bands of the speech spectrum morethan the other so as to aid in confusing an auditor.

21. The method of transmitting secret telecommunication which consistsin transmitting two superposed carrier waves of the same frequency butof different phase, modulating one carrier to form a speech spectrum,modulating the other carrier to form a screen spectrum, completelycovering one spectrum with the other, and causing the screen spectrum toosqillate between predetermined frequency llmlts.

GYSBERT FRANS VAN DIESEL.

